The present invention provides a methodology for managing power consumption in master driven time division duplex wireless network.
Mobile devices have limited energy for computing and communications because of the limited battery lifetimes. Conserving battery power in mobile devices is an important consideration in designing protocols for networks with mobile nodes. This issue should be considered through all the layers of the protocol stack, including the application layer. We have addressed the battery power conservation issue at the Media Access Control (MAC) layer.
The chief sources of energy consumption in the mobile unit considered for MAC related activities are the CPU, the transmitter, and the receiver. CPU usage in mobile devices may be reduced by relegating most of the high-complexity computation (related to media access) to the stationary network. Therefore, the focus of our work is on efficient transceiver (i.e., transmitter, receiver) usage.
The radio can operate in three modes: standby, receive and transmit. We call the mode in which the devices can receive and transmit data as active mode. In general, the radio consumes more power in the transmit mode than in the receive mode, and consumes the least power in the standby mode.
For example, the GEC Plessey DE6003[2] 2.4 GHz radio requires 1.8 W in transmit mode, 0.6 W in receive and 0.05 W in standby mode. Also, power consumption for Lucent""s 15 dBm 2.4 GHz Wavelan radio is 1.725 W in transmit mode, 1.475 W in receive mode, and 0.08 W in standby mode[3]. Thus the power consumption is much lower in the standby modes. The scheduling algorithm has to be such that the devices remain in the standby mode when there is no data to transmit or receive. A constraint of switching a device to the standby mode is that the end-to-end delays may increase and may violate the Quality of Service (QoS) parameters. Thus the scheduling algorithm has to be such that the end-to-end delays do not violate the QoS parameters.
Further, the switching of a device from active mode (when it can transmit and receive data) to standby mode has overheads as it has to communicate to other devices about its switching. Thus, frequent switching from one mode to another may lead to consumption of more power. The need of minimizing such transitions requires that the device should move to standby mode after determining the expected overhead in switching and comparing it with the power it saves by switching to the standby mode. Thus, the time for which a device goes to the standby mode should be based upon the previous traffic arrival pattern for that device, so that the end-to-end delays satisfy the QoS parameters and the switching among different power modes is not frequent.
A number of approaches for scheduling data traffic in wireless networks have been proposed earlier.
U.S. Pat. No. 5,274,841 describes methods for polling mobile users in a multiple cell wireless network. However the uplink wireless communication is done using CSMA and not TDMA, hence it is not applicable to master driven time division duplex wireless system.
U.S. Pat. No. 5,506,848 describes the demand assignment system and method for mobile users in a community of interest. U.S. Pat. No. 5,297,144 describes the reservation-based polling protocol for wireless data communications network. However, both these patents use policies that are infeasible in limited bandwidth scenario in centrally driven TDMA wireless systems as they lead to wastage of bandwidth and power as devices are in ACTIVE power mode even when they have no data to transmit or receive.
U.S. Pat. No. 4,251,865 describes a polling system for a duplex communications link is discussed where terminal units or slaves are served in fixed order. Such a distribution assumes similar traffic models at each terminal unit and is thus unsatisfactory in power and bandwidth efficiency with scarce resources available in Wireless TDD MAC systems.
In U.S. Pat. No. 6,016,311, there is a dynamic bandwidth allocation scheme which assumes an asymmetric uplink/downlink bandwidth but does not address switching devices to the standby mode and does not discuss any power considerations.
Technical paper xe2x80x9cA comparison of MAC protocols for wireless local networks based on battery power consumptionxe2x80x9d[1] discusses the power consumption of devices for various MAC strategies, but it does not take into account the packet delay and does not contribute any power optimization policy which adapts to the incoming traffic.
U.S. patent application Ser. No. 09/434,583 (issued as U.S. Pat. No. 6,680,909) discusses the MAC scheduling in Bluetooth but it considers the issues of fairness and throughput in a Bluetooth piconet with no considerations of power consumption.
U.S. patent application Ser. No. 09/535,920 (issued as U.S. Pat. No. 6,657,987) discusses Optimal scheduling of connections with-Quality of Service (QoS) constraints in a polling based Media Access Control (MAC) but it does not consider the power consumption of devices.
As indicated above, none of the patents mentioned above consider power optimization and end-to-end packet delays, which are important considerations in wireless systems.
The criteria of transition from ACTIVE to STANDBY mode and vice versa have not been addressed in any prior art.
The object of the present invention is to obviate the above drawbacks by providing a system and method for managing power consumption in master driven time division duplex wireless network using such as Bluetooth and HomeRF using Adaptive probability based Polling Interval (APPI) mechanism to determine the time period for which a device moves to the low power mode.
To achieve the said objective this invention provides a system for managing power consumption in a master driven time division duplex wireless network comprising means for optimizing power consumption while maintaining quality of service requirements for end-to-end packet delay, by adjusting the polling interval for each slave in low power mode based on the incoming traffic at the slave.
The said means comprises an Adaptive Probability based Polling Interval (APPI) mechanism for adjusting the polling interval for each slave device in low power mode.
The said mechanism for adjusting the polling interval includes means for predicting the expected arrival time for the next packet at each slave based on the distribution of the inter-arrival times for the previous packets received at that slave.
The said means for predicting the expected arrival time comprises:
means for learning the number of data bursts that arrive at each slave in particular ranges of inter-arrival times,
means for estimating the probability density function of the traffic distribution at each slave, and
means for determining the expected time interval for the arrival of the next data burst at each slave for which the probability of occurrence exceeds a defined threshold value.
The said means for learning the number of data bursts is by a means which receives and stores the number of data bursts arriving in particular ranges of inter-arrival times in entries corresponding to said inter-arrival ranges
The said means for estimating the probability density function is by a mechanism to analyze the distribution of data packets for different inter arrival time duration.
The said means for estimating the expected time interval for a defined threshold probability is described by:
P(t)=0xcexa3TASH(x)xe2x89xa6PAS
where
P(t) is the probability of arrival of a packet
TAS is the inter-arrival time
PAS is the threshold probability
H(x) is the function describing the number of observed inter-arrival times for each inter-arrival period normalized by the total number of observations.
The slave is switched from active mode to low power mode based on the condition:
(TASxe2x88x92(TAS/deadline))*PRECEIVE+(TAS/deadline)*PTRANSMITxe2x88x92TAS*PLOW POWER greater than POVERHEAD
where
TAS is the expected inter-arrival time
Deadline is the deadline of service for the slaves in active mode
PRECEIVE is the power in received mode
PLOW POWER is the power in low power mode
PTRANSMIT is the power in transmit mode
POVERHEAD is the power overhead of putting the connection into low power mode and reverting it to active mode
The said mechanism for adjusting the polling interval in low power mode is based on the tolerance of the connection of the delayed packets and is defined by
xe2x80x83P(t)=0xcexa3TPH(x)xe2x89xa6PB
where
P(t) is the probability of arrival of a packet
TP is the polling interval of the slave in low power mode
PB is the probability, which reflects the tolerance of the connection for delayed packets.
H(x) is the function defining the number of observed data bursts for each inter-arrival period normalized by the total number of observations.
The slave is switched from low power mode to active mode based on the condition
(bxe2x88x921)*TLOW POWER greater than d
where
b=the measured burst length
TLOW POWER=time in the low power mode
d=estimated maximum delay of the last packet.
The said master driven time division duplex wireless network is a Bluetooth network in which the said low power mode corresponds to the xe2x80x98SNIFFxe2x80x99 mode.
The present invention also provides a method for managing power consumption in master driven time division duplex wireless network comprising optimizing power consumption while maintaining quality of service requirements for end-to-end packet delay, by adjusting the polling interval for each slave based on the incoming traffic at the slave.
The adjusting of the polling interval is by an Adaptive Probability based Polling Interval (APPI) method for adjusting the polling interval for each slave device.
The said adjusting of the polling interval includes predicting of the expected arrival time for the next packet at each slave, based on the distribution of the inter-arrival times for the previous packets at that slave.
The predicting of the expected arrival time comprises:
learning the number of data bursts that arrive at each slave in particular ranges of inter-arrival times,
estimating the probability density function of the traffic distribution at each slave, and
determining the expected time interval for the arrival of the next data burst at each slave for which the probability of occurrence exceeds a defined threshold value.
The said learning of the number of data bursts is by a storage method which stores the number of data bursts arriving in particular ranges of inter-arrival times in entries corresponding to said inter-arrival ranges.
The said method for estimating the probability density function is defined by analyzing the distribution of data packets for different inter-arrival time durations.
The determining of estimating the expected time interval for a defined threshold probability is by:
xe2x80x83P(t)=0xcexa3TASH(x) less than PAS
where
P(t) is the probability of arrival of a packet
TAS is the inter-arrival time
PAS is the threshold probability
H(x) is the function describing the number of observed data bursts for each inter-arrival period normalized by the total number of observations.
The said determining of the expected time interval is defined by:
(TASxe2x88x92-(TAS/deadline))*PRECEIVE+(TAS/deadline)*PTRANSMITxe2x88x92TAS*PLOW POWER greater than POVERHEAD
where
TAS is the expected inter-arrival time
Deadline is the deadline of service for the slaves in active mode
PRECEIVE is the power in received mode
PLOW POWER is the power in low power mode
PTRANSMIT is the power in transmit mode
POVERHEAD is the power overhead of putting the connection into low power mode and reverting it to active mode.
The interval for adjusting the polling interval in low power mode is based on the tolerance of the connection of the delayed packets and is defined by
P(t)=0xcexa3TPH(x)xe2x89xa6PB
where
P(t) is the probability of arrival of a packet
TP is the polling interval of the slave in low power mode
PB is the probability, which reflects the tolerance of the connection for delayed packets.
H(x) is the function defining the number of observed inter-arrival times for each inter-arrival period normalized by the total number of observations.
The slave is switched from low power mode to active mode based on the condition
(bxe2x88x921)*TLOW POWER greater than d
where
b=the measured burst length
TLOW POWER=time in the low power mode
d=estimated maximum delay of the last packet.
The said master driven time division duplex wireless network is a Bluetooth network in which the said low power mode corresponds to the xe2x80x98SNIFFxe2x80x99 mode.
The instant invention further provides a computer program product comprising computer readable program code stored on computer readable storage medium embodied therein for managing power consumption in master driven time division duplex wireless network comprising computer readable program code means configured for optimizing power consumption while maintaining quality of service requirements for end-to-end packet delay, by adjusting the polling interval for each slave based on the incoming traffic at the slave.
The said configured computer readable program code means comprises an Adaptive Probability based Polling Interval (APPI) mechanism for adjusting the polling interval for each slave device.
The said computer readable program code means configured for adjusting the polling interval includes mechanism for predicting the expected arrival time for the next packet at each slave based on the distribution of the inter-arrival times for the previous packets at that slave.
The said mechanism for predicting the expected arrival time comprises:
computer readable program code means configured for learning the number of data bursts that arrive at each slave in particular ranges of inter-arrival times,
computer readable program code means configured for estimating the probability density function of the traffic distribution at each slave, and
computer readable program code means configured for determining the expected time interval for the arrival of the next data burst at each slave for which the probability of occurrence exceeds a defined threshold value.
The said computer readable program code means configured for learning the number of data bursts is by a storage means which stores the number of data bursts arriving in particular ranges of inter-arrival times in entries corresponding to said inter-arrival ranges.
The computer readable program code means for estimating the probability density function is a means for analyzing the distribution of data packets for different inter arrival time duration.
The said computer readable program code means configured for estimating the expected time interval for a defined threshold probability is defined by:
xe2x80x83P(t)=0xcexa3TASH(x)xe2x89xa6PAS
where
P(t) is the probability of arrival of a packet
TAS is the inter-arrival time
PAS is the threshold probability
H(x) is the function describing the number of observed data bursts for each inter-arrival period normalized by the total number of observations.
The said computer readable program code means configured for determining the expected time interval is defined by:
(TASxe2x88x92(TAS/deadline))*PRECEIVE+(TAS/deadline)*PTRANSMITxe2x88x92TAS*PLOW POWER greater than POVERHEAD
where
TAS is the expected inter-arrival time
Deadline is the deadline of service for the slaves in active mode
PRECEIVE is the power in received mode
PLOW POWER is the power in low power mode
PTRANSMIT is the power in transmit mode
POVERHEAD is the power overhead of putting the connection into low power mode and reverting it to active mode.
The interval for adjusting the polling interval in low power mode is based on the tolerance of the connection of the delayed packets and is defined by
P(t)=0xcexa3TPH(x)xe2x89xa6PB
where
P(t) is the probability of arrival of a packet
TP is the polling interval of the slave in low power mode
PB is the probability, which reflects the tolerance of the connection for delayed packets.
H(x) is the function defining the number of observed data bursts for each inter-arrival period normalized by the total number of observations.
The slave is switched from low power mode to active mode based on the condition
(bxe2x88x921)*TLOW POWER greater than d
where
b=the measured burst length
TLOW POWER=time in the low power mode
d=estimated maximum delay of the last packet.
The said master driven time division duplex wireless network is a Bluetooth network in which the said low power mode corresponds to the xe2x80x98SNIFFxe2x80x99 mode.